Type 55 P/N yields both a positive and a negative. You clear the negative in sodium sulfite after development. They have different speeds. I rate the positive at 80 and the negative at 40. You have a limited tonal range (Zone 7 is about top end) and no control at all over contrast. Still, some nice images can be made with it.
This is the only film made by Polaroid which yields both a positive and a negative. 4 x 5 is the largest size in which you can get it.